docs: def play_Composition(self, composition, channels=None, bpm=120):
          """Play a Composition object."""
          self.notify_listeners(self.MSG_PLAY_COMPOSITION, {'composition'
                                : composition, 'channels': channels, 'bpm': bpm})
          if channels == None:
              channels = map(lambda x: x + 1, range(len(composition.tracks)))
          return self.play_Tracks(composition.tracks, channels, bpm)